The present invention relates to a water-cooled high voltage device having: a plurality of electrical units three-dimensionally stacked in a plurality of levels, each electrical unit having a stackable frame and a plurality of electrical modules disposed at the frame; pumping means for delivering cooling water; and a pipeline network for supplying the cooling water to the electrical modules.
The water-cooled high voltage device of this type has been widely used. A water-cooled thyristor conversion device described later in an embodiment is a typical example. Along with a recent increase in power consumption, a high-voltage and large-current device is used for a power generating system, a power transforming system, an AC/DC conversion system and so on. A compact water-cooled high voltage device is desirable for easy installation. It is also desirable that the structure of the device be suitable for mass production, easy assembly, easy maintenance and repair. In response to the above needs, a method for manufacturing a high voltage device is proposed in which the device is divided into at least one type of standard electrical module for mass-production. Desired number of each type of modules are mounted on a frame to form a basic unit, that is, an electrical unit. A predetermined number of electrical units are integrally assembled and high voltage connections are performed to complete a single high voltage device.
In the high voltage device of the above arrangement, a compact device can be manufactured by appropriately designing the electrical module and the electrical unit. The installation space is thus decreased. However, the high voltage device as a whole is heated at a high temperature due to heat generated by each unit, resulting in degradation of performance of the device. Finally, the device may be broken. In order to eliminate this drawback, various cooling means are proposed. However, it is difficult to cool parts of the large-scaled high voltage device uniformly and efficiently. Temperatures of the units vary greatly as will be described below.
FIG. 1 shows a conventional water-cooled high voltage device 116 formed by stacking electrical units in two levels. In the water-cooled high voltage device 116, oblong members are electrical modules 110 of at least one type according to a standard design. Two sets of electrical modules 110 are aligned horizontally and eight electrical modules 110 are aligned vertically in each set, as shown in FIG. 1. These electrical modules 110 are mounted in a proper container. The container and thin wires are omitted so as to clearly show the arrangements of the electrical modules 110 and the pipeline network of the cooling water. This applies to the following drawings unless otherwise specified. Three conductors P, M, and N are connected to the water-cooled high voltage device 116. Eight electrical modules arranged between the conductors P and M are assembled integrally to form an upper level electrical unit 112, and eight electrical modules arranged between the conductors M and N are assembled integrally to form a lower level electrical unit 114. Although the three conductors P, M and N are illustrated in FIG. 1, the number of conductors may be arbitrarily selected in accordance with the type of device. An AC or DC voltage may be applied across the device and an AC or DC current may also flow therethrough.
Since the electrical modules 110 dissipate heat during operation, cooling water is supplied thereto. Water is usually delivered from a pump 118 which is installed underground or on the ground. The water is then cooled in a cooler 120. The cooling water rises in pipes 122a and 122b formed by an electrical insulator and is subsequently supplied from the lowest electrical modules 110 among the eight right electrical modules and the eight left electrical modules. The cooling water used for cooling the electrical modules 110 returns to the suction side of the pump 118 through pipes 122c and 122d made of an electrical insulator. The pump 118 is driven again to supply the cooling water to the electrical modules 110 which are then cooled. Since the electrical modules 110 have the same structure, the cooling water is supplied to the lower electrical modules 110 at a high pressure and in a great amount, while it is supplied to the upper electrical modules 110 at a relatively low pressure according to the above cooling system. As a result, temperature of the electrical modules at high level are higher than that of the electrical modules at low level.
FIG. 2 shows a cooling water pipeline network of the water-cooled high voltage device 116 shown in FIG. 1. The flow path of the water pipeline network in FIG. 2 correspond to that in FIG. 1. A zigzag symbol denotes a flow resistance in a corresponding portion. Reference numeral 124 denotes a flow resistance acting on the cooling water flowing through the electrical module 110. Reference numeral 126 denotes a flow resistance of the pipe 122c connecting the vertically adjacent electrical modules 110. Arrows in FIGS. 1 and 2 denote the flow of the cooling water.
In an example shown in FIGS. 1 and 2, the number of vertically arranged electrical modules 110 is small. These electrical modules are distributed and arranged in electrical units 112 and 114. The device is formed by two-level electrical units 112 and 114. Therefore, the level difference between the upper and lower electrical modules 110 is relatively small. However, in a large-scaled high voltage device, the electrical units 112 and 114 are preferably stacked at three or four levels. A thyristor conversion device which has a rated DC voltage of 125 kV and a DC current of 1,200 A (measured in a three-phase bridge circuit) is mounted in the three-phase bridge circuit, the level difference becomes 3 to 6 m. Further, when the two three-phase bridge circuits are cascade-connected, the level difference becomes 10 to 12 m. It is very difficult to uniformly cool the electrical modules 110 in different levels.
According to a graph in FIG. 3, the level of the electrical modules 110 is plotted along the axis of abscissa, while the flow rate of the cooling water flowing through the electrical module 110 as a function of the level of the electrical modules is plotted along the axis of ordinate. At point P, the flow rate of the cooling water flowing through the fourth electrical module 110 from the bottom is 0.4 times that of the cooling water flowing through the lowest electrical module. As is apparent from the graph, the upper electrical modules 110 are not sufficiently cooled. In order to solve the above problem, the diameters of the pipes 122a, 122b, 122c and 122d are enlarged to reduce the flow resistances in the pipes 122a to 122d. However, a piping work becomes cumbersome. Even if this operation is performed, the device as a whole becomes large in size. Theoretically, a flow resistance 124 within the electrical modules 110A need only be designed to be larger than a flow resistance 126 within the vertically aligned pipes 122a to 122d. However, a high output pump must be used and the cooling water pressure is increased. Therefore, highly rigid pipes and joints must be used, resulting in inconvenience.
The hydrokinetic problems in the cooling water pipeline network have been considered so far. Larger diameter pipes also result in inconvenience from the electrical point of view. The electrical modules for a high voltage are disposed at high level, while the electrical modules for a low voltage are disposed at low level. The pipes 122a to 122d vertically extend between the electrical modules at high and low levels. Therefore, parts at high and low voltages are shortcircuited by the cooling water flowing through the pipes 122a to 122d. A leakage current flows through the cooling water. The conductors on the sides of the high and low voltages are electrically corroded. This electrical corrosion frequently occurs when large diameter pipes are used and a large amount of cooling water exists between the members of the high and low voltages. Especially, this phenomenon occurs in a recently developed thyristor conversion device in which resistors, reactors and so on used in cooperation with thyristor elements are directly cooled by the cooling water. Therefore, small diameter pipes are preferably used to increase the leak resistance between the members of high and low voltages. Although a highly pure cooling water may be used to extremely decrease electrical conductivity theoretically, special equipment for maintaining an extremely low electrical conductivity is required, resulting in economic disadvantages.
It is thus strongly desired to develop a water-cooled high voltage device, which requires a small installation space, which rarely causes electrical corrosion even if water obtained from the conventional ion exchanger is used, and which substantially uniformly cool each electrical module.